The invention relates to an electrohydraulic solar panel carrier adjusting device.
It is known in the technology of solar energy, e.g. in solar power plants, to install a plurality of solar panels in fixed positions. However, fixed positions are a compromise since both the position of the sun and the energy gain from the solar panels vary. In order to optimize the energy gain it is known to let the solar panels track the path of the sun by means of an electrohydraulic adjusting device. Then the primary energy input for operating the electrohydraulic adjusting device, of course, should be less than the energy gain achieved by tracking the path of the sun. These requirements put a relatively high load on the electrohydraulic adjusting device in terms of power consumption of electrical components of the device. A further important requirement aside from the necessity to adjust the carrier at any time, even in case of an electricity breakdown or during night time into the protected position, e.g. in case of danger of a storm or strong winds, in order to avoid damage to the solar panel or the adjusting device. In order to solve this problem it is known in practice to provide an autarkic electric power source, e.g. an automobile battery, to operate the motor pump aggregate and electrical components of the adjusting device independently from the mains and even in case of a power breakdown in the mains, to then adjust the protected position. The configuration of the solar panel and its sub-structure per se is such that the weight load of the solar panel including the carrier generates a permanent force in the direction towards the protected position at the sub-structure. The weight load can be used to adjust the protected position in case of a power breakdown and without power consumption of components of the adjusting device. However, this function means a displacement of hydraulic medium between the chambers of the hydrostatic tilt motor and, in some cases, needs to even draw hydraulic medium out of the motor pump aggregate to the hydrostatic tilt motor. This has not functioned satisfactorily in practice up to now, due to e.g. the flow resistance in long connecting lines. Furthermore, when hydraulic medium was displaced between the chambers of the hydrostatic tilt motor, poorly defined hydraulic conditions resulted which make it extremely complicated to correctly re-start the adjusting device, e.g. after a power breakdown.
A hydraulic actuation assembly for a covering lid in a vehicle) known from EP-A-0 803 630, is designed such that in one embodiment the cover lid may be lowered only by the weight of the cover lid into a defined position. In this condition, a provided solenoid seat valve of the control system is de-energized. The pump is switched off. The lowering movement of the cover lid is decelerated by an aperture. The aperture can be adjusted and allows to finely tune the moving speed of the cover lid. However, an adjustment of the cover lid caused by the weight load only can be executed first when the limit pressure of a preloaded emergency valve is overcome. This complicates a rapid and safe adjustment of the cover lid.
DE-A-10 02 22 36 discloses a mechanical/hydraulic adjustment system for solar generators which track the movement of the sun about two axes. Load holding valves are arranged between the directional control valves of the hydrostatic motors and the pressure source or the tank, respectively. The load holding valves can be opened alternatively by hydraulic pilot pressure from the respective other working line. The electric motor driving the pump is supplied with electric power provided by the solar generator. In order to activate a braking system a directional control valve is arranged in a discharge line leading to the tank.
It is an object of the invention to provide an electrohydraulic adjusting device of this kind which can be operated with a small amount of electric power, which allows to adjust the protected position of the carrier even in the case of an electric power breakdown or in case that the electric power has been switched off intentionally, and which assures well-defined hydraulic conditions for a later re-start of the operation of the adjusting device.
During normal operation with sufficient available electric power the suction line is blocked. The adjusting device can be operated with low electrical input. Since the suction line is located very close to the hydrostatic tilt motor, with the monitoring solenoid automatically opening the suction line either in case of an electric power breakdown or when the electric power has been switched off intentionally, the acting weight load of the carrier and the solar panel will suffice to reliably bring the carrier relatively rapidly to the protected position, despite the fact that hydraulic medium has been displaced therefor. Since any displacement of hydraulic medium takes place between the chambers of the hydrostatic tilt motor either in case of an electric power breakdown or of an intended power switch-off, and independently from length dimensions of lines extending to the motor pump aggregate, poorly-defined hydraulic conditions will definitely be avoided for the later re-start of normal operations. The measure to permanently energize the monitoring solenoid during normal operation, and consequently open the suction line for low-resistance fluid flows in case of an electric power breakdown or when the electricity has been switched off, allows to dispense with an autarkic power supply, meaning cost reduction and fewer structures. As the monitoring solenoid has negligible power demand and does not influence normal operation of the adjusting device, the adjusting device can be operated with the minimum input of primary energy. The requirement is fulfilled easily to consume less primary energy for the sun tracking function than energy is gained by the sun tracking function.
In an expedient embodiment the permanently energized monitoring solenoid has a power consumption of only between about 1.5 volt to 6.0 volt, preferably to only about 3.0 volt. Such low power consumption of the monitoring solenoid is negligible as long as electric energy is available.
In an expedient embodiment the working lines extending between the hydrostatic tilt motor and the blocking valves or load holding valves are interconnected via a suction path from which a discharge line branches off which deviates the blocking valves or load holding valves. A respective pilot pressure operated multi-way seat valve is arranged in the suction path and in the discharge line. The multi-way seat valves are pilot-pressure operated either from the suction path or the discharge line and thus do not consume electric power during operation. A pilot circuit of both multi-way seat valves is connected to the discharge line via an unloading branch. This unloading branch contains a solenoid seat valve having the monitoring solenoid as an actuator such that in case of either an intended power switch off or an electric power breakdown the solenoid seat valve will seek an open position due to the de-energized monitoring solenoid, to then operate the multi-way seat valves into the open position. Since the open solenoid seat valve situated in the unloading branch only has to pass a very small pilot quantity of the hydraulic medium, the solenoid seat valve can be small and well-responsive which allows to use a monitoring solenoid with an extremely low power demand. In case of a hydrostatic tilt motor even with equally sized chambers the discharge line even may be dispensed with. To the contrary, i.e., in the case of differently sized chambers, the discharge line has the additional function to discharge a part of the hydraulic medium displaced between the chambers when the protected position is adjusted. With the latter-mentioned function, i.e. discharging at least a part of the hydraulic medium which is displaced between the chambers via the discharge line the hydrostatic tilt motor may be a differential cylinder the piston rod of which is fully retracted in the protected position such that the protected position is well-defined by a form-fit or a force-fit at an end position. The suction path is opened in suction direction from the piston side chamber to the piston rod side chamber such that the hydraulic medium displaced out of the piston side chamber keeps the piston rod side chamber full without creating poorly-defined hydraulic conditions, because excessive hydraulic medium from the piston side chamber directly is discharged via the discharge line e.g. to the motor pump aggregate. A hydrostatic tilt motor (one of several differential cylinders) further offers the advantages that due to differently sized pressure receiving surfaces the piston rod immediately will be extended (leaving the protected position) upon re-start of normal operation of the adjusting device, even if both working lines first have equal pressures before a true tilt control begins to work.
With a view to well-defined hydraulic conditions at the re-start of normal operation after the protected position has been adjusted, it may be expedient to arrange respective check valves in the suction path and in the discharge line with each check valve blocking in flow direction to the piston side chamber. These check valves may assist to occasionally blocking the carrier against wind load or unpredictable forces.
A further important feature is a lowering brake valve located in the discharge line. Specifically in case of a differential cylinder a partial volume has to be discharged when displacing hydraulic medium from the piston side chamber into the piston rod side chamber. The lowering brake valve accurately limits the speed of the piston into the protected position. In this way, a too rapid carrier movement can be avoided which otherwise may cause damage.
In a structurally simple way at least the suction line including the monitoring solenoid is integrated into a valve block which also contains the blocking valves or load holding valves. The valve block either is directly mounted at the hydrostatic tilt motor or is mounted at lest in direct vicinity of the hydrostatic tilt motor, i.e., in each case relatively distant from the motor pump aggregate. This structural principle is simple and saves mounting space at the hydrostatic tilt motor and assures short flow paths mainly for hydraulic medium which has to be displaced when the protected position is adjusted.
With a view to high functional safety and the minimum input of primary energy a closure member is provided in each multi-way seat valve in the suction path and in the discharge line. The closure member is loaded at an opening control side in opening direction and in closing direction at a closing control side by pilot pressure either taken from the suction path or from the discharge line. In some cases, even the respective pressure receiving surfaces of the closure member may have different sizes. Preferably, even a valve spring may be provided which urges the closure member in closing direction. The valve spring, however, may be relatively weak. Furthermore, an aperture may be provided between the suction path and the discharge line at one side and the closing control side of the respective multi-way seat valves at the other side. The closing control sides of both multi-way seat valves are connected to the monitoring solenoid actuated solenoid seat valve in the unloading branch. The closing control sides of both multi-way seat valves are connected via the solenoid seat valve in the unloading branch to a working line section extending to the motor pump aggregate. The passage cross-section of the open solenoid valve in the unloading branch is larger than the size of the respective aperture such that a pressure drop will be generated reliably and relatively rapidly by the aperture upon occurrence of an electric power breakdown or intended power switch off. This pressure drop switches the multi-way seat valves open to open the suction path and the discharge line. The hydrostatic tilt motor automatically will be smoothly brought to the protected position.
The size of the respective aperture e.g. may correspond to a bore of about 0.4 mm diameter, while the cross-section of the open solenoid seat valve may correspond to a bore of about 0.7 mm to 0.8 mm diameter instead.
Since, as mentioned, even during normal operation of the adjusting device the consumption of primary energy, i.e. electric energy, should be as low as possible, in order to maximize the energy gain resulting from the sun path tracking function. In a preferred embodiment the motor pump aggregate may contain a reversible electric motor and a pump discharging in both rotary directions. The reversible electric motor and the reversibly discharging pump so to speak may fulfil a directional control function of the adjusting device to dispense with an additional electric power-consuming solenoid actuated directional control valve. Furthermore, a pair of pilot pressure-operated ⅔-way valves and a pair of system pressure-limiting valves may be contained in the motor pump aggregate, which both operate without primary electric energy. The motor pump aggregate may be connected via a directional control slider valve either to the tilt control system of the hydrostatic tilt motor or to a rotation control system of the carrier, in order to selectively control needed adjustment steps (tilting steps or rotation steps) for the sun position tracking function. The directional control slider valve might consume electric energy, however, for the respective switchover only. The electric power consumption of the electric motor driving the pump is not changed significantly by the reversibility. The adjusting device in total can be operated with very little primary energy.
The power consumption of the solenoid of the directional control slider valve needed for the switchover between rotation steps and tilting steps may amount only to about 5 volt to 10 volt, preferably to only 8.0 volt. Expediently, the directional control slider valve then is held by spring force in the switching position for actuating the tilt control system (smaller consecutive tilting steps may be needed more often than consecutive rotation steps) and is switched over by the solenoid for a rotation step only for a short while. Overall, the principle of how the adjusting device is designed hydraulically and electrically results in an extremely favorable energy balance.
Expediently, several parallelly circuited hydrostatic tilt motors, in particular differential cylinders, may constitute the tilt control system. The motors are connected to a common tilt control. This “parallel” principle in some cases might lead to distortion of the carrier and/or the solar panel. If distortions should be excluded, several parallel hydrostatic tilt motors, in particular differential cylinders, might be used, each having a separate tilt control.
In order to assure that operation of the blocking valves or load holding valves in the respective two working lines do not consume electric energy when during normal operation hydraulic medium has to be displaced from one chamber of the hydrostatic tilt motor to the motor pump aggregate these valves expediently are controlled to open against spring force by pilot pressure taken from the respective other working line. In case of an electric power breakdown or when the adjusting device is not actuated, the blocking valves or load holding valves automatically will maintain blocking positions and hydraulically block the carrier in the initial position. For similar purposes, a hydraulically releasable braking device engaged by spring force may be provided in the rotation control system.